1. Technical Field
The present invention relates to apparatuses and methods for biological fluid analyses in general, and to the same in which a biological sample is mixed to produce a uniform distribution of constituents and/or reagents.
2. Background Information
Historically, biological fluid samples such as whole blood, urine, cerebrospinal fluid, body cavity fluids, etc. have had their particulate or cellular contents evaluated by smearing a small undiluted amount of the fluid on a slide and evaluating that smear under a microscope. Reasonable results can be gained from such a smear, but the cell integrity, accuracy and reliability of the data depends largely on the technician's experience and technique. Analysis by smear is also limited, and cannot be used for analyses such as a complete blood count (CBC).
In some instances, constituents within a biological fluid sample can be analyzed using impedance or optical flow cytometry. These techniques evaluate a flow of diluted fluid sample by passing the diluted flow through one or more orifices located relative to an impedance measuring device or an optical imaging device. Disadvantages of these techniques include that they require dilution of the sample, and fluid flow handling apparatus.
It is known that biological fluid samples such as whole blood that are quiescently held for more than a given period of time will begin “settling out”, during which time constituents within the sample will deviate from the constituent distribution present within the collected sample; e.g., deviate from a uniform distribution of constituents within the sample. If the sample is quiescently held long enough, constituents within the sample can settle out completely and stratify (e.g., in a sample of whole blood, layers of white blood cells, red blood cells, and platelets can form within a quiescent sample). Non-uniformity within the sample can also occur when adsorption occurs within a fluid passage. The term “adsorption” as used herein refers to the tendency of fluid sample, or parts thereof, to adhere to the surfaces of a fluid passage. If a large enough population of constituents within a fluid sample (e.g., platelets, RBCs, WBCs in a sample of whole blood) adheres to a fluid passage between the point of collection and the chamber in which the sample will be analyzed, the sample available for analysis could be non-representative of the sample collected. In such instances, the accuracy of the analysis could be negatively affected.
In those embodiments where it is desirable to deposit one or more reagents within the cartridge for admixing with the sample, the reagents may be in a form (e.g., particulate form, crystalline form, low solubility, etc.) that inhibits dissolution with the sample. Undissolved particles of reagent above a certain size will not be admitted into the analysis chamber, but others may pass into the analysis chamber where they can appear as debris within the sample images. Large particles of dye, for example, can create localized high concentrations of dye, which concentrations can saturate cells and make them unidentifiable. In either instance, the concentration and uniformity of the reagent within the sample can be negatively affected.
What is needed is an apparatus and a method for analyzing biological fluid samples that facilitate sample uniformity, and/or reagent uniformity within the sample.